Biomedical subjects
J M Findlay
Publications and source records attributed to J M Findlay.
In vivo animal models of cerebral vasospasm: a review.
Explore the source record for details and available documents.
Saccade target selection in visual search: the effect of information from the previous fixation.
This paper reports an analysis of saccades made during a task of visual search for a colour shape conjunction. The analysis concentrates on the saccade following the first saccade, thus complementing an earlier paper where the first saccades were analysed. The further analysis addresses the issue of what information might be held in trans-saccadic memory. As with the first saccade, incorrect second saccades tend to fall on distractors sharing one feature with the target. The proximity of the target to the fixation location immediately prior to the saccade is a very significant determinant of whether the saccade will reach the target. The results lead to the conclusion that in the majority of cases, choice of saccade destination is made afresh during each fixation with no carry-over from the previous fixation. However, in a small number of cases, second saccades are made after extremely brief fixation intervals. Although these saccades show a similar probability of reaching the target as those following longer fixations, it is argued that this sub-set of saccades are pre-programmed at the time of the preceding saccade.
Visual search in depth.
The accuracy of saccade localisation during visual search was examined for a search target defined by the single features of orientation or depth or by a conjunction of the two features. Subjects were required to move their eyes to the target which appeared in one of eight possible locations, arranged circularly around fixation, with non-targets filling the remaining seven positions. Search for a target defined by a single feature resulted in approximately 70% correct first saccades in both cases, while search for the conjunction target resulted in only 40% correct first saccades. Furthermore, averaged latency for conjunction search was longer than for simple search. Nevertheless, some subjects showed a remarkably good ability to locate a conjunction target with a single saccade of short latency. An analysis of first saccades in terms of their speed and accuracy indicates that the target selection is not preceded by a covert scanning of the display but rather is a result of parallel processing of the visual information provided. We also relate our study to the study of conjunction search reported by Nakayama and Siverman [Nakayama, K., & Silverman, G.H. (1986). Serial and parallel processing of visual feature conjunctions. Nature, 320, 264-265.].
Endovascular treatment of a lenticulostriate artery aneurysm with N-butyl cyanoacrylate.
BACKGROUND: Aneurysms arising from lenticulostriate artery branches in moyamoya-type disease are challenging lesions to treat, due to their fragility and deep location. Surgery is difficult and endovascular options may be limited. METHODS: A 57-year-old woman presented with a right ganglionic parenchymal hemorrhage due to a ruptured lenticulostriate artery aneurysm associated with ipsilateral middle cerebral artery occlusion. The aneurysm and parent feeding artery were occluded using endovascular injection of N-butyl cyanoacrylate. RESULTS: The aneurysm was successfully obliterated and although some glue did enter the more distal middle cerebral artery, there was no change in the patient's neurologic status. CONCLUSIONS: In highly selected cases where lenticulostriate aneurysms cannot be directly accessed for surgery or endovascular coiling, obliteration with liquid acrylic glue may be considered as a therapeutic option.
Current educational issues in the clinical neurosciences.
OBJECTIVE: Canadian training in the clinical neurosciences, neurology and neurosurgery, faces significant challenges. New balances are being set by residents, their associations and the Royal College of Physicians and Surgeons of Canada between clinical service, education and personal time. The nature of hospital-provided medical service has changed significantly over the past decade, impacting importantly on resident training. Finally, future manpower needs are of concern, especially in the field of neurosurgery, where it appears that soon more specialists will be trained than can be absorbed into the Canadian health care system. METHODS: A special symposium on current challenges in clinical neuroscience training was held at the Canadian Congress of Neurological Sciences in June 2000. Representatives from the Canadian Association of Interns and Residents, the Royal College of Physicians and Surgeons of Canada and English and French neurology and neurosurgery training programs made presentations, which are summarized in this report. RESULTS: Residency training has become less service-oriented, and this trend will continue. In order to manage the increasingly sophisticated hospital services of neurology and neurosurgery, resident-alternatives in the form of physician "moonlighters" or more permanent hospital-based clinicians or "hospitalists" will be necessary in order to operate major neuroclinical units. Health authorities and hospitals will need to recognize and assume this responsibility. As clinical experience diminishes during residency training, inevitably so will the concept of the fully competent "generalist" at the end of specialty training. Additional subspecialty training is being increasingly sought by graduates, particularly in neurosurgery. CONCLUSIONS: Training in neurology and neurosurgery, as in all medical specialties, has changed significantly in recent years and continues to change. Programs and hospitals need to adapt to these changes in order to ensure the production of fully qualified specialists in neurology and neurosurgery and the provision of optimal care to patients in clinical teaching units.
Combined laminectomy and thoracoscopic resection of a dumbbell neurofibroma: technical case report.
Explore the source record for details and available documents.
CT angiography for the detection and characterization of carotid artery bifurcation disease.
BACKGROUND AND PURPOSE: Computed tomographic angiography (CTA) is a relatively new and minimally invasive method of imaging intracranial and extracranial blood vessels. The main purpose of this study was to compare CTA to the current gold standard of arterial imaging, digital subtraction angiography (DSA), for the detection and quantification of carotid artery bifurcation stenosis. We also compared Doppler ultrasound (US) with these 2 techniques. METHODS: In a prospective study, 40 patients (80 carotid arteries) underwent CTA, US, and DSA. Patients chosen for inclusion were symptomatic with TIAs or stroke and had initial US screening that indicated >50% carotid stenosis on the side appropriate for the symptoms. Source axial, maximum intensity projection (MIP), and shaded-surface display (SSD) images were produced for each CTA study. The US, CTA, and DSA images were reviewed, with the degree of stenosis quantified and presence of ulcers determined; each type of imaging was reviewed by a separate investigator blinded to the results of the other 2 modalities. The results of CTA and US imaging were compared with the DSA images for degrees of carotid stenosis. RESULTS: CTA source axial images correlated with DSA more closely than MIP or SSD images for all degrees of stenosis. The correlation between US and DSA (0.808) was poorer than that between CTA and DSA (0.892 to 0.922). CTA performed well in the detection of mild (0% to 29%) carotid stenosis, as well as carotid occlusion, with values for sensitivity, specificity, and accuracy near 100%. In determining that a stenosis was >50% by DSA measurement, CTA was again useful, with a sensitivity, specificity, and accuracy of 89%, 91%, and 90%, respectively. While CTA was quite specific and accurate in identifying degrees of stenoses in either the 50% to 69% or the 70% to 99% ranges, in this task it was much less sensitive: 65% for 50%-69% stenosis and 73% for 70%-99% stenosis. These results did not change significantly when only the data from the most clinically relevant symptomatic arteries were analyzed. CTA was found to correlate quite well with DSA in the detection of ulcers associated with the carotid stenosis. CONCLUSIONS: CTA was found to be an excellent examination for the detection of carotid occlusion and categorization of stenosis in either the 0%-29% or >50% ranges. However, CTA was unable to reliably distinguish between moderate (50%-69%) and severe (70%-99%) stenosis, which is an important limitation in the investigation and treatment of carotid stenosis.
In vivo animal models of cerebral vasospasm: a review.
BACKGROUND: Cerebral vasospasm is delayed-onset cerebral arterial narrowing in response to blood clots left in the subarachnoid space after spontaneous aneurysmal subarachnoid hemorrhage (SAH). Ideally, studies on the pathogenesis and treatment of cerebral vasospasm in humans should be conducted using human cerebral arteries. Because in vivo experiments using human vessels are not possible, and postmortem pathological examination of human arteries in vasospasm provides only a limited amount of information, a number of animal models of vasospasm have been developed. METHODS: The literature was searched to find all references to in vivo animal models of SAH and vasospasm. An online search of the medical database MEDLINE was initially performed using the key words "cerebral," "vasospasm," "subarachnoid," "hemorrhage," "animal," and "model." References were checked to determine the first description of each in vivo animal model. RESULTS: Fifty-seven models of SAH and vasospasm were identified. These models used one of three techniques to simulate SAH: 1) an artery was punctured allowing blood to escape and collect around the artery and its neighbors; 2) an artery was surgically exposed, and autologous blood obtained from another site was placed around the artery; or 3) blood from another site was injected into the subarachnoid space and was allowed to collect around arteries. Each technique has advantages and disadvantages. The majority of animal models of SAH and vasospasm use intracranial arteries; however, extracranial arteries have also been used recently in vasospasm experiments. These studies seem easier and less costly to perform, but concerns exist regarding the physiological dissimilarity between systemic and cerebral arteries. CONCLUSION: The model of SAH and vasospasm used most frequently is the canine "two-hemorrhage" model, in which two injections of blood into the dog's basal cistern performed 48 hours apart result in greater arterial vasoconstriction than that effected by a single injection of blood. On the basis of its ability to accurately predict what occurs in human SAH, the best model of vasospasm seems to be the primate model in which a blood clot is surgically placed around the large cerebral vessels at the base of the monkey's brain.
Improving the appropriateness of carotid endarterectomy: results of three city-wide studies.
Explore the source record for details and available documents.
Saccade selection in visual search: evidence for spatial frequency specific between-item interactions.
We present two experiments in which subjects were required to make a saccade to a target amongst distractors. Targets were oriented Gabor patches. Analysis of errors, when subjects fail to make a saccade to the target, showed two interesting features. First, most error saccades were directed towards a distractor and not to the blank space between distractors. This suggests that although the location of the target may not be encoded correctly, the locations of the items in the display are encoded. Second, when the display items were all of the same spatial frequency, a long-range effect occurred whereby the likelihood of an error saccade in a specific direction decreased systematically as the distance from the target increases. This systematic influence of the target location extended over practically the whole display. The long-range effect appeared whenever all display items had the same spatial frequency and showed little dependence on the spatial frequency of the display items. However, when the items had different spatial frequencies the long-range effects were absent.
A model of saccade generation based on parallel processing and competitive inhibition.
During active vision, the eyes continually scan the visual environment using saccadic scanning movements. This target article presents an information processing model for the control of these movements, with some close parallels to established physiological processes in the oculomotor system. Two separate pathways are concerned with the spatial and the temporal programming of the movement. In the temporal pathway there is spatially distributed coding and the saccade target is selected from a "salience map." Both pathways descend through a hierarchy of levels, the lower ones operating automatically. Visual onsets have automatic access to the eye control system via the lower levels. Various centres in each pathway are interconnected via reciprocal inhibition. The model accounts for a number of well-established phenomena in target-elicited saccades: the gap effect, express saccades, the remote distractor effect, and the global effect. High-level control of the pathways in tasks such as visual search and reading is discussed; it operates through spatial selection and search selection, which generally combine in an automated way. The model is examined in relation to data from patients with unilateral neglect.
'Coarse-to-fine' cyclopean processing.
Previously (Popple et al, 1998 Vision Research 38 319-326) we found, using random-dot stereograms, that initial vergence increases with the size of a cyclopean disc. A corresponding improvement in stereoacuity within the disc was predicted, because disparities in the disc would be brought closer to the plane of current fixation. In the present experiment, we looked at the effect of the spatial extent of a briefly presented (< or = 500 ms) cyclopean depth pedestal on stereoacuity thresholds. Observers were required to judge the depth of a small, 1.7 deg, central disc relative to a larger surrounding disc in a random-pattern stereogram. The larger disc was set, initially, at a pedestal disparity of +/- 24 min of arc against a fixation-plane surround. The size of the larger disc was varied from 2.6 to 8.0 deg. As predicted, stereoacuity thresholds fell significantly with increasing pedestal disc size. Next, the disparity of the pedestal disc was varied. When pedestal disparity was reduced to +/- 2.4 min of arc, a disparity too small to demand vergence, the size effect disappeared except when the pedestal boundary was within 30 min of arc of the test disc boundary. We argue from this result that the effect was largely due to vergence and not cyclopean integration alone. However, the effect of pedestal size was found to persist with stimuli too brief to permit vergence (< or = 100 ms) suggesting that factors other than vergence may also play a role.
An examination of a temporal anisotropy in the visual integration of spatial frequencies.
Three pairs of experiments were conducted to investigate the importance of spatial-frequency-processing delays imposed by the visual system on the efficacy of their subsequent integration. In the first pair of experiments filtered versions of a natural image were found to be easily discriminable from the full-bandwidth image. These images were then placed into triplets and presented sequentially. Subjects were required to detect the presence of a full-bandwidth target image within the sequence. As with previous results a low-to-high progression of spatial-frequency information did increase the number of errors of full-bandwidth-image detection within the triplets where it was not present. However, this was not found across all conditions and was suggested to be due to the increased discriminability of the constituent images which form the image triplets. The second experiment was a repetition of the first with more confusable component images. Again the weak order effect on target detection was found. It was suggested that this may be due to the nature of the stimulus used. The third pair of experiments repeated the design of the first pair of experiments but with Gabor patches which provide localised spatial-frequency information. It was found that a low-to-high progression of spatial frequencies resulted in more false detections of the target. The results are interpreted as supporting an integration mechanism which operates with greater efficacy when the presentation of spatial-frequency information mirrors that naturally imposed by the neural delays involved in the processing of spatial frequencies.
Computed tomographic angiography versus digital subtraction angiography for the diagnosis and early treatment of ruptured intracranial aneurysms.
OBJECTIVE: Computed tomographic angiography (CTA) is a rapid and minimally invasive method of detecting intracranial aneurysms. We wished to determine whether CTA could replace digital subtraction angiography (DSA) in the diagnosis and operative planning of ruptured cerebral aneurysms. METHODS: In a prospective study, patients with subarachnoid hemorrhage diagnosed by plain computed tomography underwent CTA, DSA, or both. Computed tomographic scans and CTA studies were first reviewed by the treating surgeon, along with a neuroradiologist, and a decision to proceed to DSA or directly to surgery was made on the basis of the type and quality of information provided by CTA. All patients underwent postoperative DSA. RESULTS: A total of 173 patients were studied. In 24 patients, both CTA and DSA were negative for a source of subarachnoid hemorrhage. Twelve patients underwent DSA without prior CTA because a technologist capable of performing CTA was not available when the patient was evaluated. Nine patients in poor neurological condition underwent CTA, and all tested positive for aneurysms but died without surgical intervention. Of the 126 patients who underwent CTA and surgery, 65 (52%) also required preoperative DSA. The decision to proceed to DSA after CTA was influenced by aneurysm location; posterior communicating artery (62%) and posterior circulation locations (67-75%) more commonly proceeded to DSA than middle cerebral artery aneurysms (34%; 0.025 > P > 0.01). The sensitivity and specificity of CTA for the detection of all aneurysms, ruptured and unruptured, in the group of patients who underwent both types of angiograms preoperatively were 84 and 100%, respectively. In the group of 61 patients in whom aneurysm surgery was performed on the basis of CTA results alone, the sensitivity and specificity for the detection of all aneurysms, as compared with postoperative DSA, were 90 and 100%, respectively. Missed aneurysms (n = 24) were always small (<4 mm) and were usually found in patients with multiple aneurysms in whom the larger, ruptured aneurysm was identified by CTA. In one patient, the aneurysm missed by preoperative CTA would have resulted in a different operation if detected preoperatively. CONCLUSION: It is possible to proceed to ruptured aneurysm repair entirely on the basis of good-quality CTA studies that demonstrate an aneurysm consistent with the pattern of bleeding observed on plain computed tomography (48% of the patients in this series and most common middle cerebral artery aneurysms). However, detection of small unruptured aneurysms in patients with multiple lesions remains a problem.
Improving the appropriateness of carotid endarterectomy: results of a prospective city-wide study.
BACKGROUND AND PURPOSE: In light of previously reported concerns regarding carotid endarterectomy (CEA) use in our city, our goal was to determine the influence of a prospective audit and educational campaign on the performance of CEA with respect to surgical appropriateness and complication frequency. METHODS: Results of our previous audit of 291 CEAs, along with CEA practice guidelines and notification of prospective surveillance, were supplied to surgeons performing CEA in our city. After this, 184 consecutive patients undergoing CEA from September 1996 to August 1997 were followed prospectively. On the basis of blinded standardized remeasurements of angiographic carotid stenoses, CEA was classified as appropriate for patients with symptomatic carotid stenoses >/=70%, uncertain for those with symptomatic stenoses <70% or asymptomatic stenoses >/=60%, and inappropriate for patients with asymptomatic carotid stenoses <60% or preoperative neurological or medical instability. RESULTS: Forty percent of patients were asymptomatic. Compared with our prior audit, the rate of appropriate CEAs improved from 33% previously to 49% of cases in the present study (P=0.0005), uncertain indications did not change significantly (49% versus 47%; P=0.61), and inappropriate indications dropped from 18% to 4% (P=0. 00002). Perioperative stroke or death occurred in 6.4% of symptomatic patients but developed in only 2.7% of asymptomatic patients, which was improved from the 5.1% rate previously found. CONCLUSIONS: In our city, the use of a surgical audit identified areas of concern regarding CEA, and subsequent education and ongoing surveillance significantly improved the use and performance of this procedure.
Antisense preproendothelin-oligoDNA therapy for vasospasm in a canine model of subarachnoid hemorrhage.
OBJECT: The purpose of this study is twofold: 1) to test antisense genetic techniques used in the prevention of cerebral vasospasm in a canine model of subarachnoid hemorrhage (SAH), targeting the endothelin-1 (ET-1) gene; and 2) to determine if fibrinolysis of subarachnoid clot with recombinant tissue plasminogen activator (rtPA) could enhance the effect of antisense treatment. METHODS: A total of 39 dogs were studied in this experiment. Placebo (six animals), rtPA (six animals), antisense preproET-1 oligodeoxynucleotide (ASOD; five animals), or rtPA plus ASOD (combined treatment; six animals) was injected into the cisterna magna 30 minutes after a second SAH was induced on the 2nd day of the experiment. The animals were observed until Day 7, when they underwent follow-up angiography and then were killed; their basilar arteries were removed for analysis. Control animals included in this study (two animals in each group) received placebo, rtPA, ASOD, or rtPA plus ASOD without induction of SAH, or rtPA with mismatched (nonsense) preproET-1 oligodeoxynucleotide following SAH. Six additional dogs were analyzed earlier following SAH. Dogs that received placebo developed severe vasospasm (51+/-8% of baseline caliber). Administration of ASOD alone resulted in a mild reduction in vasospasm (64+/-13% of baseline caliber) and rtPA alone resulted in a moderate reduction in vasospasm (81+/-5% of baseline caliber); however, the combined therapy of rtPA plus ASOD almost completely prevented vasospasm (95+/-6%, of baseline caliber), which was significantly different from all other groups (p < 0.05). Morphological analysis of the basilar arteries yielded results similar to angiography with respect to vasospasm severity. The ASOD treatment combined with rtPA resulted in reduced ET-1 expression, as demonstrated by immunohistochemical staining of the arteries, and reduced preproET-1 levels on Day 4, as measured by reverse transcription-polymerase chain reaction. Nonsense DNA sequences had no effect on the vessels. CONCLUSIONS: Antisense preproET-1 oligodeoxynucleotide treatment, when combined with clot lysis caused by rtPA, reduced vasospasm in the canine model of SAH, and this effect appeared to be related to reduced ET-1 synthesis. The results of this experiment support a causative role for ET-1 early in the course of vasospasm development in dogs. The apparent additive therapeutic effects of antisense and fibrinolytic treatments could be due to clot lysis, which allows better delivery of oligodeoxynucleotides to arteries within the subarachnoid space.
Long-term effects of in vivo angioplasty in normal and vasospastic canine carotid arteries: pharmacological and morphological analyses.
OBJECT: A canine model of hemorrhagic vasospasm of the high cervical internal carotid artery (ICA) was used to study the long-term effects of transluminal balloon angioplasty (TBA) on the structure and function of the arterial wall. METHODS: Forty dogs underwent surgical exposure of both distal cervical ICAs, followed by baseline angiographic studies on Day 0. Dogs in Group A (20 animals) underwent simple exposure of one ICA and placement of a silicone elastomer cuff around a segment of the opposite artery. These animals underwent repeated angiography on Day 7, and then TBA was performed on the uncuffed ICA; the cuff was removed from the opposite vessel. For dogs in Group B (20 animals), blood clot-filled cuffs were placed around both ICAs, and on Day 7 angiography was repeated and TBA was performed on one randomly selected ICA. Four animals were then killed from each group, and in the remaining animals the cuffs were removed from both ICAs. On Days 14, 21, 28, and 56, four animals from each group underwent repeated angiography and were then killed to permit pharmacological and morphological analyses of the ICAs. This protocol yielded five study categories: cuffed nonblood-coated arteries not subjected to TBA, blood-coated arteries not subjected to TBA, blood-coated arteries subjected to TBA, normal arteries subjected to TBA, and control arteries obtained from the proximal ICA in each animal. The contractile responses of isolated arterial rings obtained from each ICA were recorded after treatment with potassium chloride, noradrenaline, and serotonin, whereas relaxations in response to the calcium ionophore A23187 and papaverine were recorded after tonic contraction to noradrenaline had been established. Morphological analysis was performed using scanning electron microscopy. Arteries surrounded by an empty cuff exhibited no angiographic, pharmacological, or morphological differences compared with normal arteries on any study day. Arteries surrounded by blood developed angiographically confirmed vasospasm on Day 7, with characteristic pharmacological and morphological features; resolution of these symptoms occurred by Day 21. Vasospastic arteries subjected to TBA on Day 7 remained dilated on angiographic studies, exhibited impaired responses to pharmacological agents (except for papaverine), and showed altered morphological features until Day 28. Normal arteries subjected to TBA on Day 7 remained dilated on angiographic studies, exhibited impaired responses to pharmacological agents (except for papaverine), and displayed altered morphological features until Day 14. CONCLUSIONS: These results indicate that the canine high cervical ICA model produces consistent and reproducible vasospasm that follows a similar time course to that seen in humans. When TBA is performed in vasospastic arteries, it results in an immediate functional impairment of vascular smooth muscle that lasts for 2 weeks, with resolution at 3 weeks; morphological changes are mostly resolved 3 weeks post-TBA. In normal vessels, TBA causes functional impairment and morphological alterations that are not as severe or as long-lasting as those seen in vasospastic arteries.